I just bought a 30 head and spent a few days experimenting with speaker options. It can easily drive 2 16 ohm 112 cabs, equalling the required 8 ohm load. I run a single 112 with an 8 ohm Jensen in it and the thing rocks. I will probably be forced to build a custom cab for the head after I fall in love with it. I'm in deep like after less than 2 weeks. It makes a great gig back-up for my tube 60, and with the light 112 is easier to take to the jams than the 60.
I hooked up a 212 with Governor and Hellatone, 112 with blue marvel, 112 with greenback. Ended up with the 112 jensen, just sounded best overall with the amp modeling.
The 30 head is a LOUD little sucker and sounds great. Go for it. The 15 is awesome, but not loud enuf to gig with and offers only half the effects. Vypyr mini satck will rock for sure.
I did finally hook my 75 up to my old scorpions in my renown a while back and was highly impressed I think i coulda got by with the 30watt head and used them. using the stock single 12 I have to use the octave tip we got awhile back, using the 2 scorpions its not needed at all. someday i'll update the firmware and try the global effects and see how the darker setting works maybe.
so yes 2 -12s IMO make a big differance.